As an eccentrically oscillating gear device for driving members configuring a robot; that is, robot members and the like, conventionally known is a gear device with a built-in main bearing which supports an external load that is applied to the robot members. With this kind of gear device, as described in Japanese Patent Application Publication No. 2005-47006, a carrier is rotatably mounted inside a cylindrical case via a pair of main bearings. A plurality of pin teeth are provided to an inner peripheral face of the cylindrical case. The pin teeth are sandwiched between the pair of main bearings aligned in an axial direction and their movement in the axial direction is thereby regulated. The pin teeth are pin-shaped members. An internal gear is configured as a result of the pin teeth being disposed at regular intervals on the inner peripheral face of the cylindrical case. The pin teeth can engage with external teeth of an oscillating gear which oscillates and rotates in conjunction with the rotation of the crank shaft. With the configuration of this gear device, since the pair of main bearings is housed in a case of the gear device, the robot members can be used by being respectively fixed to the case of the gear device and a carrier, and the main bearing is not required on the side of the robot member.
Here, when a pair of robot members is rotatably coupled to each other via the main bearing provided outside the gear device, the main bearing for receiving the external load of the robot members can be omitted in the gear device. With a gear device that does not have such a main bearing built therein, for example, as with the gear device described in Japanese Examined Utility Model Application Publication No. H4-29988, movement of the internal gear pins in the axial direction is regulated by providing a pair of snap rings to both upper and lower ends of the internal gear pins on the inside of the cylindrical case. Meanwhile, movement of the oscillating gear in the axial direction is regulated by the carrier as with conventional technology.
With a gear device that does not have such a main bearing built therein, variation in the assembly width of the main bearing outside the gear device that occurs due to dimensional errors of components is absorbed by the movement of the relative position of the internal gear pins and the oscillating gear.
With the gear device described in Japanese Examined Utility Model Application Publication No. H4-29988, since movement of the oscillating gear in the axial direction is regulated by the carrier, and movement of the internal gear pins in the axial direction is regulated by a snap ring on the side of the case, variation in the assembly width of the main bearing provided independently from the gear device is absorbed based on the movement of the relative position of the internal gear pins and the oscillating gear. Thus, when the relative shift amount of the internal gear pins and the oscillating gear in the axial direction is large, the contact width and the contact area of the internal gear pins and the oscillating gear will decrease and, consequently, there is a possibility that early breakage such as abnormal wear may occur (for example, refer to the internal gear pin 103 and the oscillating gear 106 shown in FIG. 7).
Moreover, since a pair of snap rings is provided in order to regulate the movement of the internal gear pins in the axial direction, the number of components of the gear device will increase.